Ultrasonic surgical handpieces include a tool that is vibrated at ultra high frequency, i.e. over 23,000 cycles per second for generating a standing wave about a distal tip thereof. The energy produced and delivered at the distal tip effects cellular material of humans and animals by fragmentation and/or emulsification. Less substantial cells are destroyed initially such that selective surgical effects and procedures are possible. The distal tip is at an end of an elongate metal tubular tool that extends from the handpiece held by the surgeon. Fragmented and/or emulsified cellular debris can be removed from the operative site with suction applied to the treated tissue. Specifically, a passage through the tubular tool connects to a source of suction through which the debris is drawn. In piezo driven tools the passage continues through the vibrator and in magnetostrictive vibrators the passage runs parallel to the vibrator. With any vibrator the electrical energy supplied to generate the axial ultrasonic vibrations applied to the tool connected thereto has a portion of the electrical energy converted to heat. Heat is thus inevitably a part of the process and has been removed by a circulating coolant flow, air cooling, debris removed through the passage or any combination thereof, Depending upon the level of energy applied and the vibrator used, the type of cooling required varies and the techniques used are distinct. Some form of cooling remains necessary at all times during the operation of the vibrator to minimize its degradation due to the heat generated during conversion of electrical energy to ultrasonic vibrations useful for surgery. In ultrasonic surgical handpieces wherein the cooling is merely a result of fluid movement through the passage of the tool and vibrator, clogging and/or choked flow presents a serious concern to the proper and successful operation of the cooling system. That is to say that, in ultrasonic surgical handpieces wherein the removal of surgical debris is a means by which the heat energy generated by the vibrator is conducted away, a supplemental cooling circuit is required to prevent destruction of the vibrator. It makes no difference if the vibrator has piezo crystals or magnetostrictive laminations so long as the handpiece operating temperature is maintained at a low level comfortable to the surgeon.
Valleylab Inc, Boulder, Colo. manufactures ultrasonic surgical instruments and has a number of assigned patents. The present disclosure is also assigned to Valleylab Inc. Three patents held by Valleylab Inc are U.S. Pat. Nos. 4,493,694; 4,516,398 and 4,921,476 which disclose and claim ultrasonic surgical handpieces and methods including pre-aspiration holes located near the distal tip of the surgical tool. Those aforementioned patents teach the preaspiration device and its technique for use and more specifically the advantages of having preaspiration holes located near the distal tip of the tool. In the device disclosed therein an irrigation flue is carried to extend distally from the handpiece and surround the tool. The extending flue provides an annular space through which irrigant may flow toward the tip. It is thought in those patents that it is preferred to have the irrigant in fluid return through the preaspiration holes for these reasons. First is to prevent flooding the operating site with irrigation fluid such that the surgeon would have to deal with that in addition to the bodily fluids resulting from surgery. Second is to prevent misting resulting when the ultrasonic vibrations of the distal tip break up the irrigation fluid into five particles and disperse them there about as vapor. Third is the use of the irrigation fluid returned through the holes near the distal tip to lubricate, facilitate and promote the flow of debris removed from the operational site thereby preventing clogging. Because the irrigation fluid returned through the holes near the distal tip passes through the piezo vibrator with the debris, cooling is provided. For magnetostrictive a separate cooling loop is required. Piezo vibrators include a passage therethrough which allows the debris and irrigant to pass therethrough during removal for cooling. Consequently, the concept and execution of the preaspiration holes serve to permit an additional function of allowing added irrigation fluid flow for vibrator cooling during surgery but not when the tool is clogged and/or semi clogged.
Several problems exist when the preaspiration holes are placed near the distal tip including tool breakage. The tool is tubular titanium shaped with a Gaussian contour in side profile to resist the stresses and strains associated with being driven to vibrate at ultrasonic frequencies by the vibrator. That is to say that, the tubular titanium tool is stretched and compressed at over twenty thousand to forty cycles per second by the application of ultrasonic vibration. Consequently, discontinuities such as holes near the distal tip act as stress concentration. Unfortunately, those stress concentrations are disposed close to an area of maximum stress and present a problem. Specifically, and on occasion the distal tip of the tubular titanium tool will fracture circumferentially through the holes and drop off. That situation is unacceptable during a surgical procedure since the failure of the tool results in the distal tip falling directly into the operative site.
Wherein the aforementioned three advantages of the preaspiration holes are not essential or desired but cooling remains a concern the use of a circulating irrigation fluid flow sufficient to cool the vibrator remains a requirement for long life and cool operation. No existing ultrasonic surgical handpiece is available or known that has a vibrator cooling circuit through the tool and about the vibrator when the tip is clogged or semi-clogged.